1. Field of the Invention
This invention relates to a low-noise level automotive internal combustion engine, and more particularly to such an engine equipped with a bearing beam structure for supporting a crankshaft in a manner to reduce engine noise level.
2. Description of the Prior Art
As a cause of engine noise, vibration noise is emitted from the cylinder block skirt or lower section and from the oil pan which noise is caused by the vibration of a cylinder block. In order to reduce such vibration noise it would seem sufficient to suppress vibration, due to explosion torque applied to the crankshaft by increasing the rigidity of the cylinder block. However, this unavoidably leads to an increase in cylinder block wall thickness and accordingly to a great increase in engine weight, thereby giving rise to new problems such as reduced fuel economy. In view of this, a variety of propositions have been made to improve the rigidity of the cylinder block while suppressing the increase in cylinder block weight. Of these propositions, attention has been paid to the employment of a bearing beam structure which securely connects a plurality of bearing caps directly supporting the crankshaft to improve the strength of the bearing caps and engine parts associated with them.